injector scaling and injector voltage latency

evopower1021 · Dec 12, 2006, 12:31 PM

i've just installed a set of precision 1000cc injectors and i'm trying to get them setup right so i can start working on the maps.. here is a conversation i've had with malibujack for anyone else that needs the info.

If your idle (low) is good and close to zero, but your mid trim (cruise trim) is still positive, then you can increase the latency at the 12.5 and 14v (approx) slightly until they are both reading about the same, whether it 5 and 5 or whatnot, as long as its the same then you can move on..
Then you cruise around a bit, if the trims are positive, it means its adding fuel, so reduce injector size a little bit, and do it again, and vice versa, if they are negative, increase the injector size slightly.

Ultimately what you will end up with is mid and low trims should read as close to zero (or 100 in evoscan) as possible, and the O2 feedback should hover around 0, with it swinging occasionally, but no more than +/-10

Finally, if your idle trims begin to drift, even though you got your long term low and mid trims in check, you can use the open loop fuel map to add or remove a little fuel until the trims are good.

Now you have the injectors properly scaled, and you can tune the open loop maps since they will be a bit whacked after you scaled the injectors.

The short hand notes..

Low trim greater than mid trim, add latency, mid trim greater than low trim, lower latency, once trims are the same, alter injector size accordingly.. Finally adjust open loop fuel maps to your desired AFR.

If you find you have to crank the engine quite a bit before it fires, or if the car swings lean when the idle speed drops (or engine load increases) then you have to look at the latency values below 14v

Jack

my question is:

where do i start adjusting on the voltage latency and how much do i adjust? i made a log and my low is at 9 and my middle is at -9. so i'm kinda stumped at where to go with this.

please post if you have any tips..

thanks
michael

PVD04 · Dec 12, 2006, 01:58 PM

With your low at +9 and your mid at -9 you should decrease your scaling and increase your latency. Make small adjustments to the latency as a little goes a long way, especially with 1000 cc injectors. A good starting point for your latency settings can be found in the larger "Injector Scaling and Latency" thread in the EcuFlash section.

-Paul

l2r99gst · Dec 12, 2006, 02:35 PM

Also, make sure that you don't have unmetered air getting in at idle and vacuum conditions, like a vented breater hose or a VTA BOV. That could cause your idle LTFTs to be much richer than cruise, due to the increased vacuum.

Eric

evopower1021 · Dec 12, 2006, 04:57 PM

thanks guys i'll try it out

coolguycooz · Dec 13, 2006, 02:11 AM

i have a question, im assuing 100 in evoscan for 02 sensor feedback is 0. What do you do if it swings more then 10+/-? how do you adjust that, also my stock even it swings about 30+/-. And my mid trim is always 3.125 while my low trim is 0. hasnt change that i noticed, and my looking at other peoples posted logs its the same for theirs? is that just the way its set up from the factory? also what do you adjust to keep your 02 sensor feedback from swining out past 10+/-?

MalibuJack · Dec 13, 2006, 07:17 AM

On the 100 scale, if it is +/- 10 its within a normal range, since its roughly 4-5% on a 0 scale.. however, short term trims (o2 feedback) are relatively condition dependent, so the LTFT Mid and LTFT low are the numbers that are important and will indicate the "average running conditions" which is where your targetting. The closer you get those to perfect, the less "swinging" the O2 feedback will do. (it does happen occasionally under different engine loads like A/C or alternator load though)

This is why the scaling in evoscan should be adjusted to match the "Standard formatting" used by OBD-II Not only is it a little confusing to offset from 100, but its roughly twice the value..

coolguycooz · Dec 13, 2006, 12:41 PM

wait so in evoscan 02 feedback is short term fuel trim? cause there is a label in evoscan that says short term fuel trim? witch one is it?

evopower1021 · Dec 13, 2006, 03:25 PM

ok i made some adjustments and now the low is 5 and the middle is -5. it doesn't seem to run any different. should i leave it as is or get it closer to 0?

l2r99gst · Dec 13, 2006, 05:46 PM

Well, that's all up to you in the end. In my opinion, +5 and -5 is fine, well within the ECUs adjustment range. But, the closer you get them to 0, the more range the ECU has for adjustments in the long run.

But, nonetheless, +5 and -5 is much better than +9 and -9.

Eric

Jeff_Jeske · Dec 15, 2006, 07:58 AM

I'm a newbie but if you aren't going as large as 1000cc inj do most people stick with stock inj size and then tweek the fuel table or do they change the scaling at the ECU level?

I'll be tossing some 850cc inj in and am looking of the best way to achieve this without having to dick with the tune very much.

MalibuJack · Dec 15, 2006, 08:11 AM

It really depends on how wacky your trims are.. There are plenty of situations where you can put in 720cc injectors and not alter the injector size or latency, but as soon as it throws off your fuel trims, you need to get them as close as possible for closed loop operation to work properly. Once their fairly close, you can clean it up with the fuel maps and tune the open loop fueling..

If you can get the fuel trims right, it means that the injectors are scaled in such a way that the AFR values used in the tables, will be somewhat similar to what your actual AFR's are... This is why its important to get close.. Its not perfect, but makes getting your brain around the values a little easier.

Jeff_Jeske · Dec 15, 2006, 08:31 AM

I'm familiar with the fuel trims as I'm coming from DSMLink. What got me going was a thread I found last night claiming dynoflash didn't change the scaling even though the customer had 720s in his car. The thread claimed that scaling didn't work properly leading to changes in AFR throughout the powerband (sometimes would be lean and sometimes be rich).

If I'm reading what you just posted correctly, I dont know how you can toss in 720 injectors not change anything and still be good to go.

MalibuJack · Dec 15, 2006, 08:40 AM

Scaling properly is important, but its not necessary since the fueling could be handled with the fuel tables.

Inconsistency can be caused by the injector latency value. I'm thinking the person describing his problem is actually a closed loop problem (part throttle driving) which can manifest itself as being inconsistently rich or lean as the fuel trims try to adjust.

It shouldnt make much difference once your in open loop, typically if that happens in open loop tables, its due to inconsistent MAF readings causing the airflow to read higher or lower and therefore altering the fueling.

The right way to go about this is to adjust the scaling and latency, but not doing it and only using the fuel tables, shouldn't cause what he's describing.

coolguycooz · Dec 15, 2006, 02:15 PM

I'm still a little confused, can somebody clear up exactly what the fuel trims are, in evoscan ? o2 feedback? or the 3 trims in evoscan, the only thing i have figured out is that 100 in evoscan means 0, but i would like somebody to clearly explain what the fuel trims are. and what these variables mean?

Fuel trim low?

Fuel trim mid?

Fuel trim high?

o2 Feedback Trim?

MalibuJack · Dec 15, 2006, 02:33 PM

O2 feedback is the immediate adjustments made on a second by second basis..

Fuel Trim Low, is a long term fuel trim for idle and low speed operation

Fuel Trim Middle is a long term fuel trim for cruising and light load driving

Fuel trim High is something I've NEVER seen change, but I think it has to do with high load idle and cruise, A/C, Alternator load, etc.. since thats the only other condition that I can think of that would logically trim differently than the others. Unfortunately since i've never noticed it change, I'm uncertain what it is really for and I'm only speculating.